Catalyst compositions similar to those of the present invention are known for the oxidation of acrolein to acrylic acid. For example, U.S. Pat. No. 3,736,354 discloses catalyst compositions containing molybdenum and vanadium that may be promoted by 17 additional elements, among which are magnesium and copper. Rhenium is not disclosed as a possible promoter to these catalysts.
U.S. Pat. No. 3,966,802 discloses a molybdenum-vanadium catalyst that may be promoted with alkali metal and optionally tungsten or antimony. The highest single pass yield of acrylic acid shown in this patent is 70.5% without the optional tungsten and 72.8% when tungsten is used as an additional promoter.
U.S. Pat. No. 3,567,773 discloses a molybdenum, vanadium and tungsten catalyst that obtains yields as high as 89% acrylic acid.
Finally, U.S. Pat. No. 4,042,533 discloses a molybdenum, vanadium, tungsten catalyst that may be promoted by one or more of the elements of rhenium and titania. The highest per pass conversion achieved with rhenium catalyst is noted as 87% acrylic acid.
The present invention is based upon the discovery that promoters that have given unacceptable yields in the prior art catalyst, when combined with molybdenum-vanadium catalyst, achieve excellent conversions of aldehydes to acids.